In one type of vacuum assembly, a device of interest is hermetically sealed into the interior of a vacuum housing. The interior of the vacuum housing is evacuated, either during the sealing operation or subsequently through a vacuum line that is then sealed. The interior of the vacuum housing is not further evacuated by a pump during storage or service. Such sealed vacuum units are often used when the volume, weight, and/or power requirements of a pump that is available during storage and service are not consistent with the application.
During the sealing operation, during storage, or during service, additional gases may be evolved from the device or from the interior walls of the vacuum housing, or slowly leaked into the interior of the vacuum housing. The additional gases may include inorganic gases such as oxygen or nitrogen, or organic evolved gases. If these additional gases are allowed to continue to accumulate, their concentration may eventually become so great that the device may no longer be operable at the increased gas pressure, or other problems such as increased convective heat flow may arise.
One technique for reducing the concentration of the additional gases is to place a getter material that is highly reactive with the additional gases into the interior of the vacuum housing. As the additional gases are produced in the interior of the vacuum housing, the getter material chemically reacts, as by forming a solid reaction product, or physically reacts, as by adsorbing, the additional gases. The concentration and partial pressure of the additional gases remains low. An example of a known getter material is titanium.
The getter material is usually deposited upon a getter substrate. Typical getter materials must be activated by heating to a moderate activation temperature such as in the range of 500-900° C., before they can function to getter the additional gases. To accomplish the activation, the usual practice is to pass an electrical current through the getter substrate, ohmically heating the getter substrate and thence the getter material to the required activation temperature. During the elevated-temperature activation and even subsequently during service, some of the getter material may sputter or otherwise leave the getter and deposit upon other components such as the interior of windows or the device itself, interfering with their subsequent operation. Also, the radiant energy produced during the getter activation may heat and damage sensitive internal devices. To prevent such deposition of the getter material onto the other components and to prevent excessive heating by radiant energy during activation of the getter material, a getter shield may be positioned between the getter material and the other components, so that the evaporated getter material and the radiant energy fall on the getter shield rather than on the other components.
Available getter shields are relatively large in size and weight, and difficult to assemble with the getter assembly and the other components in the interior of the vacuum housing. The problem is of particular concern for miniaturized structures. There is accordingly a need for a better approach for preventing undesirable deposition of getter material on other components and excessive heating of other components in evacuated structures. The present invention fulfills this need, and further provides related advantages.